The present invention relates to a control system for controlling an electromagnetically operated valve, and more particularly to an electromagnetic valve control system which is capable of executing a soft landing of a movable member onto an electromagnet in a valve open/close control.
Lately, there are proposed various electromagnetic valve operating systems that employ an electromagnetic actuator comprised of a movable member, a pair of electromagnets and a pair of springs so as to reciprocatingly operate intake and exhaust valves of an internal combustion engine. Generally, it is preferable that a movable member of such a valve operating system is softly landed on an electromagnet while ensuring a required motion performance. A Japanese Patent Provisional Publication No. (Heisei)11-159313 discloses a landing method for softly landing a movable member on an electromagnet in an electromagnetic valve operating system. Such soft landing in this system is achieved by temporally switching off the electromagnet during a period between a switch-on moment of the electromagnet and the landing moment of the movable member. Further, in order to realize a further accurate landing control of an electromagnetic valve unit including a valve and an electromagnetic actuator, there is proposed a control method employing a characteristic representative of a vibration system of the electromagnetic valve unit.
However, the characteristic of the vibration system of the controlled electromagnetic valve unit is varied according to an operating condition. Particularly, a friction in the electromagnetic valve unit is largely affected by a temperature since the friction largely depends on a characteristic of rubricating oil whose viscosity is varied according to the change of temperature. Therefore, it is difficult to stably execute a required landing control only by a preset characteristic representative quantity.
It is therefore an object of the present invention to provide a control system for certainly executing a soft landing control of an electromagnetic valve unit by employing an actual characteristic of a vibration system of the electromagnetic valve unit.
An aspect of the present invention resides in a valve control system comprising an electromagnetic valve unit and a controller. In this system, the electromagnetic valve unit comprises a valve, a pair of electromagnets arranged in spaced relationship from one another in axial alignment with the valve so as to form a space, a movable member axially movably disposed in the space between the electromagnets and interlocked with the valve, and a pair of springs biasing the movable member so as to locate the movable member at an intermediate portion of the space when both of the electromagnets are de-energized. The controller is connected to the electromagnetic valve unit and energizes and de-energizes each of said electromagnets to reciprocatingly displace the valve. The controller is arranged to detect a characteristic of a free vibration of a vibration system in the electromagnetic valve unit when both electromagnets are de-energized, and to estimate at least one of a friction quantity and a spring constant of the vibration system on the basis of the detected characteristic of the free vibration.
Another aspect of the present invention resides in a method for controlling an electromagnetic valve unit, the electromagnetic valve unit being arranged to operate a valve by electromagnetically controlling a pair of electromagnets so as to displace a movable member disposed in a space between the electromagnets which receiving biasing force of a pair of springs. The method comprises detecting a characteristic of a free vibration of a vibration system in the electromagnetic valve unit when both electromagnets are de-energized; and estimating at least one of a friction quantity and a spring constant of the vibration system on the basis of the detected characteristic of the free vibration.